- 'Ecological
stoichiometry' -- Ratio of elements in plankton and other
organisms (oceanographer
Redfield in the 1950's)
- Found an average phytoplankton composition of
(Redfield Ratio)
C
H
O
N
P S
106 263
110
16
1
0.7
- Compared with available nutrient ratios
- He considered P to be the most limiting
nutrient
even though it is only
~1% organic matter
BECAUSE the amount of P available to organisms is much less than the
amount required
relative to these other elements
- Also implies that if nothing else is limiting, then increasing P can
theoretically generate >100X
the weight of added P in algae

5. No gas phase
i. phosphine (PH3) gas may be produced by bacterial
action
under strongly reducing conditions
ii. spontaneously combusts
iii. may be responsible for will-o'-the-wisps, moving lights over
swamps
and marshes

8. Decomposition and
excretion
i. well-developed, efficient recycling of P
ii. P excreted by animals is rapidly taken up by algae and bacteria
iii. often one major function of decomposition is the liberating of
usable
P
iv. Lack of oxygen due to decomposition actually feeds back and affects
the availability of PO43- through some
more redox reactions.

II. Redox reactions

- P doesn't go through
redox
reactions itself, but it is influenced by the solubility of Fe, which
changes
due to its redox state

A. Iron trap for P
- In oxygenated waters,
iron is present as Fe3+ (ferric)
- At pH<7 you get
-- vivianite
- At pH> or equal to 7
you
get
-
stratified lake day of turnoverone week later

-
What happens?
i. Fe2+ is converted to Fe3+ due to presence of
oxygen
ii. Fe3+ goes to Fex(OH)y(PO4)z
,
FeOH, and FePO4
- "iron trap for P", less available for algae
- Can be a critical point for eutrophication -- when
hypolimnion
becomes anoxic, then more P is released and that increases the P
recycling and loading from within the lake as well -- contributes to
increased
eutrophication.
- As long as hypolimnion remains oxic, any phosphate in sediments will
be trapped by iron trap as it comes to the sediment
surface, even if the sediments are anoxic.

B. Sulfur trap for iron

- If enough FeS
precipitates
you can remove enough Fe to get iron poor water and so at overturn more
P is available for algal uptake
- "Sulfur trap for iron"
- increases phosphate
release,
because reduces the potential iron trap

SUMMARY OF REDOX EFFECTS ON PHOSPHATE CONCENTRATIONS:

- Fe3+
conversion
to Fe2+ releases PO43-
- sulfur trap may lower
iron concentrations enough to allow some phosphate to remain at
overturn
- All these reactions
mediated
by bacteria